A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.
Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more important factor for enabling miniature IC or other devices and/or structures to be manufactured.
A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1):
                    CD        =                              k            1                    ⋆                      λ                          NA              PS                                                          (        1        )            where λ is the wavelength of the radiation used, NAPS is the numerical aperture of the projection system used to print the pattern, k1 is a process dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NAPS or by decreasing the value of k1.
In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation sources are configured to output a radiation wavelength of about 13 nm. Thus, EUV radiation sources may constitute a significant step toward achieving small features printing. Such radiation is termed extreme ultraviolet or soft x-ray, and possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or synchrotron radiation from electron storage rings.
In known lithography apparatus, the substrate can be held by a substrate holder during the lithographic process. The average temperature of the substrate holder can vary during use. For example, during a certain period of time, the average temperature of the substrate holder can rise, for example by heating caused by incoming exposure radiation during exposure sequences and/or due to heating caused by nearby actuators or motors. This can lead to a temperature offset between the substrate and the substrate holder, which temperature offset may result in substrate distortion and/or overlay errors.
In known lithography apparatus, a patterning structure (reticle) can be held by a respective patterning structure holder during the lithographic process. Just after being transferred to the patterning structure holder, in the known apparatus and method, the patterning structure temperature rises (for example from room temperature to several degrees above room temperature), due to being irradiated by incoming exposure radiation. A resulting temperature offset between the patterning structure and the patterning structure holder, which temperature offset may result in distortion of the patterning structure, strain in the patterning structure, and overlay errors.
European Patent Application No. 1770445A1 proposes a lithographic apparatus arranged to transfer a pattern from a patterning structure onto a substrate, including a substrate holder configured to hold a substrate, and a substrate temperature conditioner configured to condition a temperature of the substrate prior to, during, or both, a transfer of the substrate to the substrate holder to substantially match a temperature of the substrate holder. In the known apparatus, the substrate temperature conditioning system may include a substrate support, located in a substrate handler, which support can be thermally controlled to bring the temperature of a substrate supported thereon to a desired temperature.